Stepped photoresist profile and opening formed using the profile

ABSTRACT

Stepped photoresist profiles provide various methods of forming profiles in an underlying substrate. The stepped photoresist profiles are formed in two layers of photoresist that are disposed over the substrate. The substrate is then etched twice using a respective opening in each photoresist layer to create a stepped profile in the substrate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to integrated circuits and, moreparticularly, to a photoresist technique for use in fabricatingintegrated circuits.

2. Description of the Related Art

Integrated circuits, such as microprocessors and memory devices, areused in a wide variety of applications. Such applications includepersonal computers, industrial control systems, telephone networks, anda host of consumer products, just to name a few. As most people areaware, an integrated circuit is a highly miniaturized electronic circuitthat has revolutionized the functionality, dependability, and size ofthese various products.

In the manufacturing of integrated circuits, numerous microelectroniccircuits are simultaneously fabricated on a semiconductor substrate.Such substrates are typically referred to as wafers, and a typical waferincludes a number of different regions, known as die regions. When thefabrication of the integrated circuits on the wafer is complete, thewafer is cut along these die regions to form individual die. Each diecontains at least one microelectronic circuit, which is usuallyreplicated on each die.

Although often referred to as semiconductor devices, integrated circuitsare in fact fabricated from numerous materials of varying electricalproperties. For example, integrated circuits are typically built upon abase substrate which is commonly made of semiconductive or insulativematerial. The characteristics of the base substrate may be altered, byetching or doping for instance, and various materials, such asinsulators, dielectrics, conductors, and semiconductors, may bedeposited on the base substrate in various patterns to form the finalintegrated circuit.

Of particular interest in this disclosure is the formation of openingsin a portion of the substrate of the integrated circuit. Such openingsare typically formed by fabricating a structure in a layer of insulativeor dielectric material. Such structures may include, for instance,trenches, contact openings, vias, or containers. These variousstructures are used in most integrated circuits to form contacts betweenvarious circuit elements or to create various circuit elements.

Such structures are typically formed using a photolithographic process.Photolithography is a transfer process where the pattern on a photomaskis replicated in a radiation-sensitive layer on the surface of thesubstrate. In a photolithographic process, a layer ofradiation-sensitive material is deposited over the substrate, such asthe base substrate or one or more other layers that have been depositedon the base substrate. For instance, when using ultraviolet (UV) lightas the radiation source, photoresist, which is a UV-sensitive polymer,is used as the radiation-sensitive layer.

After the photoresist has been deposited onto the substrate, thesubstrate is placed in an exposure system, and the photomask pattern tobe transferred is aligned with any existing patterns on the substrate.The photoresist is then exposed to UV radiation through the photomask.The radiation changes the structure of the photoresist in a manner thatdepends upon whether the photoresist type is positive or negative.Negative photoresist becomes polymerized, i.e., cross-linked, in areasexposed to the radiation, whereas, in a positive photoresist, thepolymer bonds are broken upon exposure. In either case, the photoresistis not affected in regions where the photomask is opaque. Afterexposure, the photoresist is developed to dissolve the unpolymerizedregions, while the polymerized portions of the photoresist remain intactto form a photoresist pattern on the substrate which is essentiallyidentical to the pattern on the photomask.

After the photoresist pattern is formed on the surface of the substrate,portions of the substrate underlying the openings in the photoresistlayer may be etched to form holes in the substrate, or dopants may bediffused or implanted into the exposed portions of the substrate. Inregard to the first possibility, e.g., etching, it may be desirable toremove a portion of the substrate along a given profile. For example, itmay be desirable to remove a portion of the substrate in a directiondirectly perpendicular to the surface of the substrate. In such asituation, an anisotropic etch may be performed. Alternatively, it maybe desirable to remove a portion of the substrate that underlies thephotoresist along the edges of the photoresist along with the exposedregion. In this circumstance, an isotropic etch may be used, as it tendsto undercut the photoresist.

However, it may also be desirable to create a stepped profile, e.g., atapered or wine glass-shaped profile, in the underlying substrate. Inthis instance, the deeper portions of the hole in the substrate arenarrower than the upper portions of the hole in the substrate. To createthis type of stepped hole, a first photoresist pattern having a smallhole is created over the substrate, and a first etching step isperformed. Thereafter, a second photoresist pattern is created either byredeveloping the first photoresist layer using a different photomask orby removing the first photoresist layer and forming a second photoresistlayer having larger openings. Once the revised photoresist pattern hasbeen created, a second etching step is performed. Alternatively, thewider opening my be etched first such that it stops on an etch stoplayer, and then the smaller opening may be etched.

This method is undesirable because it requires additional developmentsteps, possibly including two complete photolithographic steps. Also,two photomasks are required, thus causing possible alignment problems.

The present invention may address one or more of the problems set forthabove.

SUMMARY OF THE INVENTION

Certain aspects commensurate in scope with the originally claimedinvention are set forth below. It should be understood that theseaspects are presented merely to provide the reader with a brief summaryof certain forms the invention might take and that these aspects are notintended to limit the scope of the invention. Indeed, the invention mayencompass a variety of aspects that may not be set forth below.

In accordance with one aspect of the present invention, there isprovided a method of forming a hole in a substrate. The method includesthe acts of: (a) forming a lower layer of photoresist over thesubstrate; (b) forming an upper layer of photoresist over the lowerlayer of photoresist; (c) forming a first opening in the upper layer ofphotoresist; (d) forming a second opening in the lower layer ofphotoresist; (e) etching a first portion of the substrate through thefirst opening and the second opening to form a first hole in thesubstrate having a first width; and (f) etching a second portion of thesubstrate through at least the second opening to form a second hole inthe substrate having a second width, the second width being greater thanthe first width.

In accordance with another aspect of the present invention, there isprovided a method of forming a hole in a substrate. The method includesthe acts of: (a) forming a lower layer of photoresist over thesubstrate; (b) forming an upper layer of photoresist over the lowerlayer of photoresist; (c) forming a first opening having a first widthin the upper layer of photoresist; (d) forming a second opening having asecond width in the lower layer of photoresist, the first width beinggreater than the second width; (e) etching a first portion of thesubstrate through the first opening and the second opening to form afirst hole in the substrate having the second width; (f) widening thesecond opening to at least the first width; and (g) etching a secondportion of the substrate through the first opening and the secondopening to form a second hole in the substrate having at least the firstwidth.

In accordance with a further aspect of the present invention, there isprovided a method of forming a hole in a substrate. The method includesthe acts of: (a) forming a lower layer of photoresist over thesubstrate; (b) forming an upper layer of photoresist over the lowerlayer of photoresist; (c) forming an first opening having a first widthin the upper layer of photoresist; (d) forming a second opening having asecond width in the lower layer of photoresist, the first width beingless than the second width; (e) etching a first portion of the substratethrough the first opening and the second opening to form a first hole inthe substrate having the first width; and (f) etching a second portionof the substrate through the first opening and the second opening toform a second hole in the substrate having the second width.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other advantages of the invention will become apparentupon reading the following detailed description and upon reference tothe drawings in which:

FIG. 1 illustrates a block diagram of an exemplary processor-baseddevice;

FIG. 2 illustrates a cross-sectional view of an exemplary substratehaving two layers of photoresist thereon;

FIG. 3 illustrates a cross-sectional view of FIG. 2 wherein a steppedprofile has been formed in the two layers of photoresist;

FIG. 4 illustrates a cross-sectional view of FIG. 3 with a hole formedin portion of the substrate;

FIG. 5 illustrates a cross-sectional view of FIG. 4 with a second holeformed in a portion of the substrate;

FIG. 6 illustrates a perspective view of a thin-film transistor havingan elevated channel which confines the carriers to pockets along thesidewalls of the transistor; and

FIG. 7 illustrates a perspective view of a stepped resist pattern usedto form the transistor of FIG. 6.

DESCRIPTION OF SPECIFIC EMBODIMENTS

Turning now to the drawings, and referring initially to FIG. 1, a blockdiagram depicting an exemplary processor-based device, generallydesignated by the reference numeral 10, is illustrated. The device 10may be any of a variety of different types, such as a computer, pager,cellular telephone, personal organizer, control circuit, etc. In atypical processor-based device, a processor 12, such as amicroprocessor, controls many of the functions of the device 10.

The device 10 typically includes a power supply 14. For instance, if thedevice 10 is portable, the power supply 14 would advantageously includepermanent batteries, replaceable batteries, and/or rechargeablebatteries. The power supply 14 may also include an A/C adapter, so thatthe device may be plugged into a wall outlet, for instance. In fact, thepower supply 14 may also include a D/C adapter, so that the device 10may be plugged into a vehicle's cigarette lighter, for instance.

Various other devices may be coupled to the processor 12, depending uponthe functions that the device 10 performs. For instance, a userinterface 16 may be coupled to the processor 12. The user interface 16may include buttons, switches, a keyboard, a light pin, a mouse, and/ora voice recognition system, for instance. A display 18 may also becoupled to the processor 12. The display 18 may include an LCD display,a CRT, LEDs, and/or an audio display. Furthermore, an RFsubsystem/baseband processor 20 may also be coupled to the processor 12.The RF subsystem/baseband processor 20 may include an antenna that iscoupled to an RF receiver and to an RF transmitter (not shown). Acommunications port 22 may also be coupled to the processor 12. Thecommunications port 22 may be adapted to be coupled to a peripheraldevice 24, such as a modem, a printer, or a computer, for instance.

Because the processor 12 controls the functioning of the device 10generally under the control of software programming, memory is coupledto the processor 12 to store and facilitate execution of the program.For instance, the processor 12 may be coupled to volatile memory 26,which may include dynamic random access memory (DRAM) and/or staticrandom access memory (SRAM). The processor 12 may also be coupled tonon-volatile memory 28. The non-volatile memory 28 may include a readonly memory (ROM), such as an EPROM, to be used in conjunction with thevolatile memory. The size of the ROM is typically selected to be justlarge enough to store any necessary operating system, applicationprograms, and fixed data. The volatile memory, on the other hand, istypically quite large so that it can store dynamically loadedapplications. Additionally, the non-volatile memory 28 may include ahigh capacity memory such as a disk or tape drive memory.

As is clear from the above discussion, the device 10 may include one ormore semiconductor devices, such as a microprocessor or an integratedcircuit memory. It is the fabrication of such semiconductor devices thatthe remainder of this disclosure discusses. More specifically, ofparticular interest is the formation of substrate openings havingtapered or wine glass-shaped profiles, such as a dual damascenestructure. However, as discussed previously, known photolithographictechniques for creating such structures exhibit certain problems.Accordingly, FIGS. 2-10, which are described below, illustrate variousexamples of a stepped photoresist profiles along with various examplesof openings and other structures that may be fabricated using steppedphotoresist profiles.

Before specifically discussing FIGS. 2-10, it should be understood thatin the interest of clarity not all features of an actual implementationof an integrated circuit fabrication process are described. Theillustrative embodiments discussed below are restricted to those aspectsof an integrated circuit fabrication process related to the formation ofa stepped resist profile and the subsequent formation of a steppedopening in the underlying substrate. Conventional details of integratedcircuit fabrication processing are not presented as such details arewell known in the art of integrated circuit fabrication.

Turning now to FIGS. 2-5, a portion of an integrated circuit device 30is illustrated during successive stages of fabrication. Specifically,FIGS. 2-5 illustrate the fabrication of a stepped photoresist patternand a stepped opening in an underlying substrate, such as a dielectriclayer. Referring initially to FIG. 2, a substrate is illustrated andgenerally designated using a reference numeral 32. In this example, thesubstrate 32 includes a semiconductive region 34, such as a siliconwafer, which has a dielectric layer 36, such as an oxide or nitride,formed thereon. Of course, it should be understood that the material ofthe substrate 32 may vary depending upon the particular integratedcircuit being fabricated. For instance, the substrate 32 may begenerally homogeneous in that it may be primarily composed of asemiconductive material or an insulative material. Alternatively, thesubstrate 32 may be non-homogeneous in that it may represent the upperportion of a partially fabricated integrated circuit which may contain avariety of different materials. Furthermore, the substrate 10 mayrepresent a generally homogeneous portion of a generally non-homogeneoussubstrate, such as a dielectric portion of a partially fabricatedintegrated circuit.

To form a stepped photoresist profile, two layers 38 and 40 of aphotoresistive material are deposited over the substrate 32. Althoughthe layers 38 and 40 of photoresistive material may be deposited in aconventional manner, certain considerations should be noted. Forexample, a layer of photoresist is typically spun onto the surface of asubstrate. However, once the first layer 38 of photoresistive materialhas been deposited on the substrate 32, it is possible that thedeposition of the second layer 40 of photoresistive material maycompromise the integrity of the desired dual layer structure. Forexample, if the solvent system of the second layer 40 of photoresistivematerial is similar to the solvent system of the first layer 38 ofphotoresistive material, the deposition of the second layer 40 ofphotoresistive material may dissolve at least a portion of the firstlayer 38 of photoresistive material.

One method of avoiding this problem is to select photoresistivematerials having different solvent systems so that depositing the secondlayer 40 of photoresistive material does not dissolve the first layer 38of photoresistive material. Alternatively, a layer of a suitable barriermaterial (not shown), such as polyvinyl alcohol, may be deposited overthe first layer 38 of photoresistive material prior to the deposition ofthe second layer 40 of photoresistive material. Regardless of whetherthe solvent systems of the layers 38 and 40 of photoresistive materialare similar or different, the barrier layer should facilitate thedeposition of the second layer 40 of photoresistive material withoutdissolving the first layer of photoresistive material.

After the two layers 38 and 40 of photoresistive material have beendeposited on the substrate 32, the layers 38 and 40 are exposed anddeveloped to create a stepped profile, such as the profile illustratedby way of example in FIG. 3. Because the developing process utilizessolvents to dissolve the portions of exposed photoresistive material tocreate the openings 42 and 44 in the respective layers 38 and 40, theuse of photoresistive material having different solvent systems and/orhaving sufficiently different sensitivities may facilitate the formationof the stepped photoresist profile.

To create the stepped profile, the upper layer 40 of photoresistivematerial is exposed and developed to create a relatively large opening42, and the lower layer 38 of photoresistive material is exposed anddeveloped to create a relatively smaller opening 44. For example, asingle photomask with a controlled exposure may be used to expose thelayers 38 and 40, and the openings 42 and 44 may be formed during asingle development step. Alternatively, a first photomask may be used toexpose one of the layers 38 and 40, and a second photomask may be usedto expose the other layer. Then, the openings 42 and 44 may be formedduring a single development step. As yet another alternative, the upperlayer 40 may be exposed and developed to create the opening 42, and,afterward, the lower layer 38 may be exposed and developed to create theopening 44.

Once the stepped photoresist profile formed by the openings 42 and 44has been created, a portion of the substrate 32 underlying the openings42 and 44 may be removed by etching, for instance, as illustrated inFIG. 4. As a first example, the holes 46 and 48 may be created during asingle etching procedure. In this situation, the etchant erodes thephotoresistive material at the edges of the openings 42 and 44, and,eventually, substantially removes the portion of the lower layer 38 ofphotoresistive material which underlies the larger opening 42. Beforethe lower layer 38 of photoresistive material is removed, the etchantremoves a portion of the dielectric layer 36 underlying the smalleropening 44 to form the hole 46. As the etchant removes the portion ofthe lower layer 38 of photoresistive material which underlies the largeropening 42, the etchant begins to remove a wider area of the dielectriclayer 36 underlying the larger opening 42 to form the hole 48. Thus,this single etching step will approximately create the illustratedstepped profile.

In an alternative example, a first etch may be performed using anetchant that leaves the lower layer 38 of photoresistive substantiallyin tact while it removes a portion of the dielectric layer 36 exposed bythe small opening 44 in the layer 38 of photoresistive material tocreate a hole 46. The hole 46 may extend down to the substrate 34, asillustrated, or it may stop above the substrate 34 as shown by thedashed line 47. The hole 46 may be created by a wet or dry etch which isisotropic or anisotropic, depending upon the desired characteristics ofthe hole 46. Once the hole 46 has been formed, a second etch isperformed to remove a portion of the lower layer 38 of photoresistivematerial which underlies the larger opening 42 in the upper layer 48 ofphotoresistive material. As illustrated in FIG. 5, this etching stepwidens the opening 44 to be commensurate in size with the opening 42.Because a greater area of the underlying substrate 32 is now exposed,etching removes a wider portion of the dielectric layer 36 to create ahole 48. As illustrated in FIG. 5, the hole 48 extends along a portionof the length of the hole 46 and is greater in dimension than the hole46 to create the desired stepped profile in dielectric layer 36.

Of course, it should be understood that the illustrated stepped profileis somewhat idealized for the purposes of this discussion. Those skilledin the art will recognize that the actual profile will likely moreclosely resemble the wine glass-shaped profile illustrated by the dashedlines 49A and 49B depending upon the rate of resist removal during theetching procedure.

After the stepped profile has been created in the dielectric layer 36,the remaining portions of the layers 38 and 40 of photosensitivematerial may be removed. Then, the stepped hole may be filled with anappropriate material, such as a conductive material to create a contactor a buried contact, or such as one or more thin layers to createanother structure.

Finally, it should be noted that a stepped photoresist profile may beused to create circuit elements, such as the transistor 90 illustratedin FIG. 6. The transistor 90 has an elevated channel 92 which lies abovethe main portion of the substrate 94. The elevated channel 92 includesdoped regions 96 and 98 that are confined to pockets along the sidewallsof the elevated channel. The transistor 90 is completed by fabricating asource contact 100, a gate contact 102, and a drain contact 104. Due tothe elevated channel 92 and the confinement of the doped regions 96 and98, the transistor 90 may exhibit better on/off ratios than aconventional transistor.

To create the transistor 90 illustrated in FIG. 6, a stepped resistpattern is formed of two resist layers 110 and 112, as illustrated inFIG. 7, in much the same manner as described in the previously discussedexamples. The structure is then etched essentially to transfer thestepped pattern into the substrate 94 to form the elevated channel 92illustrated in FIG. 6.

While the invention may be susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, it should be understood that the invention is not intended tobe limited to the particular forms disclosed. Rather, the invention isto cover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the followingappended claims.

What is claimed is:
 1. A method of forming a hole in a substrate, themethod comprising the following acts performed in the recited order: (a)forming a lower layer of photoresist over the substrate; (b) forming anupper layer of photoresist over the lower layer of photoresist; (c)forming a first opening in the upper layer of photoresist; (d) forming asecond opening in the lower layer of photoresist; (e) etching a firstportion of the substrate through the first opening and the secondopening to form a first hole in the substrate having a first width; and(f) etching a second portion of the substrate through at least thesecond opening to form a second hole in the substrate having a secondwidth, the second width being greater than the first width.
 2. Themethod, as set forth in claim 1, wherein act (d) comprises the act of:exposing and developing the lower layer of photoresist exposed by thefirst opening.
 3. The method, as set forth in claim 1, wherein act (e)comprises the act of: anisotropically etching the first portion of thesubstrate.
 4. The method, as set forth in claim 1, wherein act (f)comprises the act of: anisotropically etching the second portion of thesubstrate.
 5. The method, as set forth in claim 1, wherein act (f)comprises the act of: isotropically etching the second portion of thesubstrate.
 6. The method, as set forth in claim 1, wherein act (f)further comprises the act of: removing the upper layer of photoresistprior to etching the second portion of the substrate.
 7. The method, asset forth in claim 1, wherein act (f) comprises the act of: etching thesecond portion of the substrate through the first opening and the secondopening.
 8. The method, as set forth in claim 7, wherein the act ofetching the second portion of the substrate through the first openingand the second opening comprises the act of: widening the second openingprior to etching the second portion of the substrate.
 9. A method offorming a hole in a substrate, the method comprising the acts of: (a)forming a lower layer of photoresist over the substrate; (b) forming anupper layer of photoresist over the lower layer of photoresist; (c)forming a first opening having a first width in the upper layer ofphotoresist; (d) forming a second opening having a second width in thelower layer of photoresist, the first width being greater than thesecond width; (e) etching a first portion of the substrate through thefirst opening and the second opening to form a first hole in thesubstrate having the second width; (f) widening the second opening togreater than the first width; and (g) etching a second portion of thesubstrate through the first opening and the second opening to form asecond hole in the substrate having at least the first width.
 10. Themethod, as set forth in claim 9, wherein act (d) comprises the act of:exposing and developing the lower layer of photoresist exposed by thefirst opening.
 11. The method, as set forth in claim 9, wherein act (e)comprises the act of: anisotropically etching the first portion of thesubstrate.
 12. The method, as set forth in claim 9, wherein act (f)comprises the act of: widening the second opening to the first width.13. The method, as set forth in claim 9, wherein act (g) comprises theact of: anisotropically etching the second portion of the substrate. 14.The method, as set forth in claim 9, wherein act (g) comprises the actof: isotropically etching the second portion of the substrate.
 15. Themethod, a s set forth in claim 9, wherein act (g) further comprises theact of: forming the second hole having the first width.
 16. The method,as set forth in claim 9, wherein act (g) comprises the act of: formingthe second hole having a width greater than the first width.
 17. Themethod, as set forth in claim 10, wherein the acts are performed in therecited order.
 18. A method of forming a hole in a substrate, the methodcomprising the following acts performed in the recited order: (a)forming a lower layer of photoresist over the substrate; (b) forming anupper layer of photoresist over the lower layer of photoresist; (c)forming an first opening having a first width in the upper layer ofphotoresist; (d) forming a second opening having a second width in thelower layer of photoresist, the first width being less than the secondwidth; (e) etching a first portion of the substrate through the firstopening and the second opening to form a first hole in the substratehaving the first width; and (f) etching a second portion of thesubstrate through the first opening and the second opening to form asecond hole in the substrate having the second width.
 19. The method, asset forth in claim 18, wherein act (d) comprises the acts of: exposingand developing the lower layer of photoresist exposed by the firstopening; and isotropically etching the lower layer of photoresist. 20.The method, as set forth in claim 18, wherein act (e) comprises the actof: anisotropically etching the first portion of the substrate.
 21. Themethod, as set forth in claim 18, wherein act (f) comprises the act of:isotropically etching the second portion of the substrate.
 22. A methodof forming a hole in a substrate, the method comprising the acts of: (a)forming a lower layer of photoresist over the substrate; (b) forming anupper layer of photoresist over the lower layer of photoresist; (c)forming a first opening having a first width in the upper layer ofphotoresist; (d) forming a second opening having a second width in thelower layer of photoresist, the first width being greater than thesecond width; (e) etching a first portion of the substrate through thefirst opening and the second opening to form a first hole in thesubstrate having the second width; (f) widening the second opening to atleast the first width; and (g) etching a second portion of the substratethrough the first opening and the second opening to form a second holein the substrate having a width greater than the first width.
 23. Themethod, as set forth in claim 22, wherein act (d) comprises the act of:exposing and developing the lower layer of photoresist exposed by thefirst opening.
 24. The method, as set forth in claim 22, wherein act (e)comprises the act of: anisotropically etching the first portion of thesubstrate.
 25. The method, as set forth in claim 22, wherein act (f)comprises the act of: widening the second opening to the first width.26. The method, as set forth in claim 22, wherein act (f) comprises theact of: widening the second opening to greater than the first width. 27.The method, as set forth in claim 22, wherein act (g) comprises the actof: anisotropically etching the second portion of the substrate.
 28. Themethod, as set forth in claim 22, wherein act (g) comprises the act of:isotropically etching the second portion of the substrate.
 29. Themethod, as set forth in claim 22, wherein act (g) further comprises theact of: forming the second hole having the first width.
 30. The method,as set forth in claim 22, wherein the acts are performed in order.
 31. Amethod of forming a hole in a substrate, the method comprising thefollowing acts performed in the recited order: (a) forming a lower layerof photoresist over the substrate; (b) forming an upper layer ofphotoresist over the lower layer of photoresist; (c) forming a firstopening having a first width in the upper layer of photoresist; (d)forming a second opening having a second width in the lower layer ofphotoresist, the first width being greater than the second width; (e)etching a first portion of the substrate through the first opening andthe second opening to form a first hole in the substrate having thesecond width; (f) widening the second opening to at least the firstwidth; and (g) etching a second portion of the substrate through thefirst opening and the second opening to form a second hole in thesubstrate having at least the first width.
 32. The method, as set forthin claim 31, wherein act (d) comprises the act of: exposing anddeveloping the lower layer of photoresist exposed by the first opening.33. The method, as set forth in claim 32, wherein act (e) comprises theact of: anisotropically etching the first portion of the substrate. 34.The method, as set forth in claim 31, wherein act (f) comprises the actof: widening the second opening to the first width.
 35. The method, asset forth in claim 31, wherein act (f) comprises the act of: wideningthe second opening to greater than the first width.
 36. The method, asset forth in claim 31, wherein act (g) comprises the act of:anisotropically etching the second portion of the substrate.
 37. Themethod, as set forth in claim 31, wherein act (g) comprises the act of:isotropically etching the second portion of the substrate.
 38. Themethod, as set forth in claim 32, wherein act (g) further comprises theact of: forming the second hole having the first width.
 39. The method,as set forth in claim 31, wherein act (g) comprises the act of: formingthe second hole having a width greater than the first width.